This.
It cuts both ways as well.
The YM are totally isolated from the YW, their leaders, organization, goals, activities. The two groups are totally isolated from each other. The YW barely get a Bishopric member with them. The YM NEVER get interaction with YW.
The way things are organized makes church and other youth gatherings more like a Jewish wedding. You don't need a rope down the middle of the room because there will be NO interaction between the sexes!! I don't like that and it has been VERY difficult to break down that wall.
Additionally, It's hard to find a Bishop who fits every need. Leader, minister, advisor/counselor, judge, decision maker, etc... As well as someone young/active/healthy enough to do things with the Priest aged YM that are desired.